Power control device, power supply device, and power control method
A power control device for performing switching control for an output voltage of a power supply device includes a signal generation circuit for comparing a difference between a value of the output voltage and a value of a first reference voltage with a value of a second reference voltage, and for stopping the switching control when a value of the difference is less than or equal to the value of the second reference voltage, and an adjuster circuit for adjusting the second reference voltage based on a ratio between a value of an input voltage and the value of the output voltage.
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This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-119475, filed on May 18, 2009, the entire contents of which are incorporated herein by reference.
FIELDThe embodiments discussed herein relate to a power control device, a power supply device, and a power control method.
BACKGROUNDDC-DC converter control techniques may include a pulse width modulation (PWM) control in which an output voltage is controlled to be constant by changing a pulse width while maintaining a constant frequency, and a pulse frequency modulation (PFM) control in which an output voltage is controlled to be constant by changing a clock cycle while maintaining a constant pulse width. For example, the PFM control is performed in a mode in which a frequency is changed continuously, or in a mode in which a frequency is changed by excluding a clock used in the PWM control. A switching frequency may be controlled in both modes.
In the PWM control, switching operations are performed per cycle even when a load is high or low. When the load is low, the amount of power consumed for the switching operations is relatively large compared with the amount of power that is supplied, and power supply efficiency may be reduced. Thus, the PWM control may be unsuitable when the load is low. In the PFM control, generally, a frequency range that may be changed (the switching frequency) is not limited. However, when a width in which the frequency is changed increases, broadband radiation noise is generated. For these reasons, a DC-DC converter may be operated in the PWM control when the load is high, and may be operated in the PFM control when the load is low. Japanese Patent Application Laid-Open Publication No. 2003-219637 discusses that frequent switching of driving operations may be reduced by making a difference between a level set when the PWM control is switched to the PFM control and a level set when the PFM control is switched to the PWM control.
A power supply device including an error amplifier may detect an output voltage, perform a switching control based on a difference between the value of the output voltage and the value of a reference voltage, and adjust the output voltage. Operational conditions of such a power supply device may change depending on a ratio between the value of an input voltage and the value of an output voltage. As a result, a difference between the value of an output voltage of an error amplifier and the value of another reference voltage may fail to satisfy given conditions even when an operating mode of the power supply device actually needs to be switched. In this case, it may be difficult to switch the operating mode under desired operating conditions.
SUMMARYAccording to an aspect of the embodiments, a power control device for performing switching control for an output voltage of a power supply device includes a signal generation circuit for comparing a difference between a value of the output voltage and a value of a first reference voltage with a value of a second reference voltage, and for stopping the switching control when a value of the difference is less than or equal to the value of the second reference voltage, and an adjuster circuit for adjusting the second reference voltage based on a ratio between a value of an input voltage and the value of the output voltage.
The object and advantages of the various aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
In the following descriptions, many of the exemplary aspects are shown to include n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) in a variety of configurations. While MOSFET devices are used as an example, the disclosed circuits may be implemented using any number of other transistor types, such as J-FETs and bipolar transistors, among others. Additionally, while n-channel devices are used in the following exemplary aspects, the same general approaches may also apply to circuits incorporating p-channel FETs or PNP bipolar transistors, for example.
Still further, while terms “drain” and “source” are used for ease of explanation and to adhere to traditional engineering usage, it should be recognized that a drain and source of a FET transistor may be considered interchangeable, and for the following descriptions merely thought of as a first end and a second end of a semiconductor channel unless otherwise stated or apparent to one of ordinary skill in the art.
An example of a power supply device is described below with reference to
As illustrated in
In the power supply device in
An outside configuration of the power control device 100 is described below.
As illustrated in
As further illustrated in
Any one of the resistor R1, the resistor R2, the PMOS transistor M1, and the NMOS transistor M2 may be included in an inside configuration of the power control device 100. A voltage of the terminal FB1 may be referred to for an input to a terminal FB2 (not depicted).
The inside configuration of the power control device 100 in
The feedback terminal FB1 is coupled to an inverting input terminal of an error amplifier ERA1. A non-inverting input terminal of the error amplifier ERA1 receives the first reference voltage (VREF1). The error amplifier ERA1 used herein may be a typical operational amplifier.
As further illustrated in
The high load implies that the amount of a coil current (IL) is large, and the low load implies that the amount of the coil current (IL) is small. As the set value is larger, the load is higher. As the set value is smaller, the load is lower. A large amount of the coil current (IL) is desired to maintain the output voltage (VOUT) at a high level.
As further illustrated in
As further illustrated in
As further illustrated in
As further illustrated in
As further illustrated in
The slope compensation circuit SP in
The slope compensation is performed to reduce subharmonic oscillation. The occurrence of the subharmonic oscillation is generally unwelcome in a typical power supply device because when the subharmonic oscillation occurs, the current flow through a coil may become unstable and broadband emission noise may be generated from the coil. The subharmonic oscillation may occur when the duty ratio is 50% or more.
Operations of the power supply device in
As illustrated in
As further illustrated in
When the transistor drive circuit SWD enters the reset state, the transistor drive circuit SWD outputs high-level signals from the output terminals Q1 and Q2 and maintains the output signals. As a result, the PMOS transistors M1 and M3 are turned off, the NMOS transistor M2 is turned on, and the current supply based on the input voltage (VIN) is stopped.
When the oscillator 2 outputs the high-level cycle signal (CS) again, the transistor drive circuit SWD reenters the set state. As further illustrated in
When the transistor drive circuit SWD repeats entering the set and reset states, a drain-source voltage (VA) of the NMOS transistor M2 periodically changes. When the oscillator 2 outputs the cycle signal (CS), the change cycle of the drain-source voltage (VA) of the NMOS transistor M2 depends on the output cycle of the cycle signal (CS). The set state of the transistor drive circuit SWD is referred to as an “ON period,” and the reset state of the transistor drive circuit SWD is referred to as an “OFF period” hereinafter. The proportion of the ON period of the transistor drive circuit SWD in one operational cycle of the cycle signal (CS) is referred to as the “duty ratio.” A period corresponding to the one operational cycle is represented by T in
The duty ratio may be obtained by dividing the set value of the output voltage (VOUT) by the value of the input voltage (VIN). Since the set value tends to be large with a high load, the ratio of the set value to the value of the input voltage (VIN) is close to 1:1, and the value of the duty ratio is large when the load is high. Since the set value tends to be small with a low load, the ratio of the set value to the value of the input voltage (VIN) deviates from 1:1, and the value of the duty ratio becomes small when the load is low.
When the value of the input voltage (VIN) is double the set value in the power supply device in
For example, the voltage (VE0) may transition, from a state in which the voltage (VE0) is higher than or equal to the second reference voltage (VREF2) and the load is high, into a state in which the voltage (VE0) is lower than the second reference voltage (VREF2) and the load is low. When the slope compensation is performed, a time period that the comparator CMP2 typically takes to output the low-level signal and a time period that the oscillator 2 typically takes to stop the output of the cycle signal (CS) may be longer compared with a case where the slope compensation is not performed.
The present invention discusses a configuration in which an increase in the time period that the oscillator 2 typically takes to stop the output of the cycle signal (CS) may be reduced or prevented even when slope compensation is performed.
As illustrated in
As further illustrated in
As illustrated in
As further illustrated in
As further illustrated in
Operations of the first adjuster circuit 1 in
As further illustrated in
Still referring to
Advantages of the first adjuster circuit 1 in
As illustrated in
Referring to
As further illustrated in
Operations of the second adjuster circuit 5 in
Still referring to
As further illustrated in
Advantages of the second adjuster circuit 5 in
A power supply device according to the second embodiment is described below with reference to
In the second embodiment in
As illustrated in
In the second embodiment in
As illustrated in
Operations of the second embodiment in
As the ratio of the output voltage (VOUT) to the input voltage (VIN) approaches 1:1, the duty ratio of the drain-source voltage (VA) of the NMOS transistor M2 increases. As the duty ratio of the drain-source voltage (VA) of the NMOS transistor M2 increases, the value of the voltage obtained by the smoothing increases. As the ratio of the value of the output voltage (VOUT) to the value of the input voltage (VREF2) approaches 1:1, the value of the second reference voltage (VREF2) increases.
The second adjuster circuit 5 according to the first embodiment in
According to the configurations obtained by the above-described combinations, the duty ratio becomes 50% or more, the value of the second reference voltage (VREF2) increases depending on the slope compensation, and as the slope compensation is performed for a longer time, the value of the second reference voltage (VREF2) increases.
The voltage (VE0) is an example of a difference. The oscillator 2 is an example of a signal generation circuit. The current (IIN) is an example of a current proportional to an input voltage. The current (IOUT) corresponds to a current proportional to an output voltage. A circuit 6 including the resistor RIN and the NMOS transistor M4 (see
According to the aspects described above, another reference voltage may be adjusted based on the ratio between the input voltage value and the output voltage value. Thus, the switching operations may be stopped by adjusting the another reference voltage even when the operational conditions change based on the ratio between the input voltage value and the output voltage value.
Although the aspects in accordance with aspects of the present invention are numbered with, for example, “first,” “second,” or “third,” the ordinal numbers do not imply priorities of the embodiments. Many other variations and modifications will be apparent to those skilled in the art.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the aspects of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the aspects of the invention. Although the embodiments in accordance with aspects of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from the context, the phrase “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form.
Claims
1. A power control device for performing switching control for an output voltage of a power supply device, the power control device comprising:
- a signal generation circuit configured to receive a second reference voltage and a difference between a value of the output voltage and a value of a first reference voltage, compare the difference with the second reference voltage, and stop the switching control when a value of the difference is less than or equal to the value of the second reference voltage; and
- an adjuster circuit configured to receive an input voltage and the output voltage, adjust the second reference voltage based on a ratio between a value of an input voltage and the value of the output voltage and output an adjusted second reference voltage to the signal generation circuit as the second reference voltage.
2. The power control device according to claim 1, wherein the adjuster circuit increases the value of the second reference voltage as the ratio of the value of the output voltage to the value of the input voltage approaches 1:1.
3. The power control device according to claim 2, wherein the adjuster circuit increases the value of the second reference voltage when the value of the input voltage becomes less than or equal to a twofold value of the output voltage.
4. The power control device according to claim 2, wherein the adjuster circuit comprises:
- a first input circuit configured to generate a current proportional to the input voltage;
- a second input circuit configured to generate a current proportional to the output voltage; and
- a computing circuit configured to compute the ratio of the value of the output voltage to the value of the input voltage.
5. The power control device according to claim 1, wherein the switching control is a step-down peak current control including slope compensation.
6. A power supply device, comprising:
- a switch configured to supply power from an input end of the power supply device to an output end of the power supply device based on switching control;
- a signal generation circuit configured to receive a second reference voltage and a difference between a value of an output voltage and a value of a first reference voltage, compare the difference with the second reference voltage, and stop the switching control for the switch when a value of the difference is less than or equal to the value of the second reference voltage; and
- an adjuster circuit configured to receive an input voltage and the output voltage, adjust the second reference voltage based on a ratio between a value of an input voltage and the value of the output voltage and output an adjusted second reference voltage to the signal generation circuit as the second reference voltage.
7. The power supply device according to claim 6, wherein the adjuster circuit increases the value of the second reference voltage as the ratio of the value of the output voltage to the value of the input voltage approaches 1:1.
8. The power supply device according to claim 7, wherein the adjuster circuit increases the value of the second reference voltage when the value of the input voltage becomes less than or equal to a twofold value of the output voltage.
9. The power supply device according to claim 7, wherein the adjuster circuit comprises:
- a first input circuit configured to generate a current proportional to the input voltage;
- a second input circuit configured to generate a current proportional to the output voltage; and
- a computing circuit configured to compute the ratio of the value of the output voltage to the value of the input voltage.
10. The power supply device according to claim 6, wherein the switching control is a step-down peak current control including slope compensation.
11. A power control method for performing switching control for an output voltage of a power supply device, the power control method comprising:
- receiving a second reference voltage and a difference between a value of the output voltage and a value of a first reference voltage;
- comparing the difference with a value of a second reference voltage;
- receiving an input voltage and the output voltage to adjust the value of the second reference voltage based on a ratio between a value of an input voltage and the value of the output voltage and output an adjusted second reference voltage to be subjected to the comparing as the second reference voltage; and
- stopping the switching control when a value of the difference is less than or equal to the value of the second reference voltage.
12. The power control method according to claim 11 further comprising increasing the value of the second reference voltage as the ratio of the value of the output voltage to the value of the input voltage approaches 1:1 during the adjusting.
13. The power control method according to claim 12 further comprising wherein increasing the value of the second reference voltage when the value of the input voltage becomes less than or equal to a twofold value of the output voltage during the adjusting.
14. The power control method according to claim 12 further comprising:
- generating a current proportional to the input voltage;
- generating a current proportional to the output voltage; and
- computing the ratio of the value of the output voltage to the value of the input voltage.
15. The power control method according to claim 11 further comprising switch-controlling a step-down peak current and slope compensation.
16. The power supply device according to claim 1, wherein the signal generation circuit includes a comparator that compares the difference with the second reference voltage.
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Type: Grant
Filed: May 12, 2010
Date of Patent: Sep 24, 2013
Patent Publication Number: 20100289471
Assignee: Fujitsu Semiconductor Limited (Yokohama)
Inventors: Toshihiko Kasai (Kasugai), Hidenobu Ito (Kasugai)
Primary Examiner: Bao Q Vu
Application Number: 12/778,812
International Classification: G05F 1/10 (20060101); G05F 1/652 (20060101); G05F 1/44 (20060101);